1. Field of the Invention
This invention relates generally to battery charging systems and methods, and more particularly to a method for detecting battery removal or absent battery conditions for a constant current charger.
2. Description of the Prior Art
Current state of the art commercially available battery charge control IC""s do not offer a means to distinguish between an absent battery or battery removal conditions without use of additional external stimulus. Typical solutions qualify battery presence with a thermistor or data input from the battery. U.S. Pat. No. 6,104,303, issued Aug. 15, 2000 to Katada, et al., entitled Battery detecting device for a radio pager, for example, uses a secondary battery and additionally requires a third electrode to sense removal or absence of a primary battery.
In view of the foregoing, a need exists for a means to efficiently detect battery absence or removal from a charging unit without use of external stimulus such as a thermistor, EEPROM, or additional pins (electrodes), and which can be used to correctly annunciate the current state of the charger to a host or end-user.
The present invention is directed to a technique that provides an efficient means to detect a battery removal from a battery charger, or otherwise distinguish between the condition when a battery is not present in the charger without the use of external stimulus. According to one embodiment, the techniques comprises a circuit having a series of logic gates arranged in a manner to produce a signal (NOBAT), that is indicative of an absent battery or battery removal state. The circuit is applied such that information provided by only the charger positive and negative terminals can be used to correctly annunciate the current state of the charger to a host or end-user. The circuit is implemented as part of a battery charger control integrated circuit (IC) that interrogates the charger output, including the current flowing through the charger to either provide a status signal or otherwise provide an input to a state machine capable of controlling the charger.
In one aspect of the invention, a technique is implemented to detect a battery removal from a charger without use of external stimulus.
In another aspect of the invention, a technique is implemented to distinguish between the condition when a battery is not present in a charger without use of external stimulus.
In yet another aspect of the invention, a technique is implemented to distinguish between the absent battery or battery removal conditions associated with a charger via information provided only by the charger positive and negative terminals.
In still another aspect of the invention, a technique is implemented to correctly annunciate the current state of a charger to a host or end-user without use of external stimulus.